Testing apparatus and method of deriving young&#39;s modulus from tensile stress/strain relationships

ABSTRACT

A method of testing and a tester apparatus to determine the axial stress and strain of cements under the temperature and pressures encountered by cement during use in wellbore environments. Using these stress and strain measurements, the Young&#39;s Modulus may be established for a material at the encountered temperature and pressure of the wellbore. By combining static tensile strength testing and elasticity measurements of cements, Young&#39;s Modulus values for different cement compositions under stresses that are similar to the conditions occurring in an actual wellbore are possible.

FIELD OF THE INVENTION

The invention relates to testing methods and devices used for testing of the mechanical properties of cement including cement formed in wellbore environments.

BACKGROUND OF THE INVENTION

Cement is used in the casing and liners of a wellbore. The annular space between the casing/lining and the wellbore is filled with a predetermined quantity of a cement mixture, which after hardening retains the casing/liner in place in the wellbore. The cement mixture is pumped in at the top end of the casing or liner, down to the lower end thereof and out into and up the annular space on the outside of the casing/liner.

Cementing is employed during many phases of wellbore operations. For example, cement may be employed to cement or secure various casing strings and/or liners in a well. Cementing may also be used to repair casing and/or to achieve formation isolation. Additionally, cementing may be employed during well abandonment. Cement operations performed in wellbores under these high stress conditions present problems including difficulty in obtaining wellbore isolation and maintaining the mechanical integrity of the wellbore.

In essence, cement is placed in the annulus created between the outside surface of a pipe string and the inside formation surface or wall of a wellbore in order to form a sheath to seal off fluid and/or solid production from formations penetrated by the wellbore. Cementing allows a wellbore to be selectively completed to allow production from, or injection into, one or more productive formations penetrated by the wellbore. Cement may be used for purposes including sealing off perforations, repairing casing leaks, plugging back or sealing off the lower section of a wellbore, or sealing the interior of a wellbore during abandonment operations.

Once established, this isolation may be impacted by the particular stresses associated with the environment found in the wellbore during operations. The cement sheath may be exposed to stresses imposed by well operations such as perforating, hydraulic fracturing, or high temperature-pressure differentials.

Furthermore, well cement compositions may be brittle when cured. These cement compositions may fail due to tensional and compressional stresses that are exerted on the set cement. These wellbore cements may be subjected to axial, shear, and compressional stresses. Relatively high temperatures may induce stress conditions and/or relatively high fluid pressures encountered inside cemented wellbore pipe strings during operations such as perforating, stimulation, injection, testing, or production. Moreover, stress conditions may be induced or aggravated by fluctuations or cycling in temperature or fluid pressures during similar operations. In addition, variations in temperature and internal pressure of the wellbore pipe string may result in radial and longitudinal pipe expansion and/or contraction which tends to place stress on the annular cement sheath existing between the outside surface of a pipe string and the inside formation surface or wall of a wellbore. In other cases, cements placed in wellbores are subjected to mechanical stress induced by vibrations and impacts resulting from operations.

Therefore, a need exists to be able to test the mechanical properties of cement such as the cement that is used in wellbore environments. This testing method needs to be able to accommodate the conditions that are found in the wellbore environment. The following testing method fail to provide a method of testing under these conditions.

Several testing methods have been developed to test various aspects of cement or concrete. For example, ASTM International has established the Standard Test Method for Flexural Strength of Concrete (Using Simple Beam With Center-Point Loading), Designation No. C 293-02. This test method purports to cover the determination of the flexural strength of concrete specimens by the use of a simple beam with center-point loading. The mechanism in this test employs a load-applying block and two specimen support blocks. Force is applied perpendicular to the face of the specimen until the specimen fails. The modulus of rupture is calculated as: R=3 PL/2 bd ²   (1) where:

R=Modulus of rupture, psi, or MPa,

P=maximum applied load indicated by the testing machine, lbf, or N,

L=span length, in., or mm,

b=average width of the specimen at the fracture, in., or mm, and

d=average depth of the specimen a the fracture, in., or mm.

This testing method only provides a modulus of rupture based on a perpendicular force being applied in surface ambient conditions. This testing method therefore fails to simulate the stresses encountered in the higher temperature and pressure conditions of the wellbore environment.

Additional standards have been developed for testing cement. For example ASTM International Standard Test Method for Flexural Strength of Hydraulic-Cement Mortars, Designation No. C 348-02 provides a centerpoint loading such that forces are applied to the specimen in a vertical direction to determine the flexural strength from the total maximum load as follows: S_(f)=0.0028 P   (2) where

S_(f)=flexural strength, Mpa, and

P=total maximum load, N.

This testing method only provides a flexural strength based on a vertical force being applied in surface ambient conditions to cause a total maximum load. This testing method therefore also fails to simulate the stresses encountered in the higher temperature and pressure conditions of the wellbore environment.

The standards also include a testing method to measure splitting tensile strength. For example ASTM International Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens, Designation No. C 496-96 provides for applying a diametrical compressive force along the length of a cylindrical concrete specimen until failure of the specimen. The loading induces tensile stresses on the plane containing the applied load and relatively high compressive stresses in the area around the applied load. Tensile failure occurs rather than compressive failure because the areas of load application are in a state of triaxial compression. The splitting tensile strength of the specimen is calculated by the formula: T=2P/(Πl d)   (3) where:

T=Tensile splitting strength, psi (kPa),

P=maximum applied load indicated by the testing machine, lbf (kN),

Π=3.1416

l=length, in. (m), and

d=diameter, in. (m).

Similarly to the previously discussed testing methods, this testing method only provides a tensile splitting strength based on a diametrical compressive force applied in surface ambient conditions. This testing method therefore fails to simulate the stresses encountered in the higher temperature and pressure conditions of the wellbore environment.

Additionally, each of these standards specifically instructs the creation of the specimens at a temperature and pressure that is similar to ambient surface conditions. None of these testing methods provides for the creation of samples under the temperature and pressure conditions found in a wellbore environment.

Therefore a need exists for the formation and testing of cement under a simulation of the conditions found in a wellbore environment. Testing methods under these conditions will provide data that is more precise in providing for a method to determine the mechanical characteristics of the specimen.

SUMMARY OF THE INVENTION

Most cements fail in the annulus of a well while under tension or a combination of tension and compression (flexural stress). The ratio of axial stress to axial strain (Young's Modulus) needs to be examined when the axial stress is tensional or a combination of tension and compression.

The present invention offers a method of testing and a tester designed to test the stress and strain of cements under the temperature and pressures encountered by cement during use in wellbore environments. Using these stress and strain measurements, the Young's Modulus may be established for a material at the encountered temperature and pressure of the wellbore. Using this information, it is possible to derive a baseline for materials to be used in the wellbore environment.

Before conducting an induced stress analysis for a given cement system, it is important to quantify the mechanical properties of that set cement. Chief among these properties is the Young's Modulus of elasticity, which is defined by the ratio of axial stress to axial strain. Typically, for a given change in well conditions, the lower the Young's Modulus is for a cement system, the lower the induced stress on that cement will be. Accordingly, the elastic nature exhibited by cement under stress, but prior to mechanical failure, is as important for long-term annular isolation, as the actual maximum stress at which mechanical failure ultimately occurs. The present invention overcomes the problems associated with a conventional static Young's Modulus test, which is a time-consuming operation and is almost always done with the axial stress applied in a compressive mode—even though by most definitions, the Young's Modulus is a mechanical property pertaining to a materials response under tension.

The following provides a means to combine static flexural/tensile strength testing and elasticity measurements of cements. Since most cements fail in the annulus of a well while under tension, or a combination of tension and compression, the ratio of axial stress to axial strain is an important factor when the axial stress was in tension, or a combination of tension and compression instead of just testing in compression. Using a testing device based on these methods, the present invention can generate Young's Modulus values for different cement compositions under stresses that are similar to the conditions occurring in an actual wellbore. The present invention allows the user to calculate the induced stresses that would occur if the different systems were used in a well, and thus develop better fit for purpose designs.

The present invention includes the development of a testing apparatus that enables the user to first cure from a liquid state, and then determine the mechanical properties such as tensile strength of various cement slurry systems through non-ultrasonic, destructive methods, while maintaining confining pressure and temperature on the cement specimens for the duration of the curing and testing process. It is within the scope of the invention that the present apparatus allows for a more accurate testing of mechanical properties of oil and gas well cements to ensure the long term integrity of the cement sheath in a well bore for the entire operation life of a given well.

Since current ASTM testing is carried out under atmospheric conditions, this invention provides for an alternative means to accurately measure tensile strength of various cement systems under more realistic field conditions. The invention discloses an apparatus that allows for the elimination of data influenced by factors such as cooldown and depressurization of cured cement samples.

Devices employing the testing techniques of the present invention may be fully automated in such a way that real-time stress versus strain plots can be generated prior to the determination of ultimate mechanical failure values. This would allow for an increase in both the quantity and the quality of data presented to the clients. Moreover, the present invention provides for data consistency and reliability because a more uniform testing method for all cement systems can be employed and all test conditions and data recording may be microprocessor controlled. The multi-functionality of this apparatus allows the user to measure cement shear bond strength while maintaining confining pressure and temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention, and, together with the description, serve to explain the principles of the invention. In the drawings:

FIG. 1 is a representative diagram of an embodiment of a modified ASTM testing device that can test tensile strength, or with a different fixture, can test flexural strength;

FIG. 2 is a diagram showing a component of the present invention;

FIG. 3 is a diagram showing a component of the present invention;

FIG. 4 is a diagram showing a component of the present invention;

FIG. 5 is top assembly view of an embodiment of the present invention showing the mold body and components;

FIG. 6 is a side assembly view of an embodiment of the present invention showing the mold body and components;

FIG. 7. is top assembly view of another embodiment of the present invention showing a plurality of mold bodies and components;

FIG. 8 is a front view of a view of an embodiment of the present invention showing the mold and components in a pressure cylinder;

FIG. 9 is a representative graph showing deflection versus time;

FIG. 10 is a representative graph showing stress versus deflection;

FIG. 11 is a representative graph showing Young's Modulus versus deflection;

FIG. 12 is a representative graph showing deflection versus time;

FIG. 13 is a representative graph showing stress versus deflection;

FIG. 14 is a representative graph showing stress versus microstrain;

FIG. 15 is a representative graph showing stress versus deflection;

FIG. 16 is a representative graph showing stress versus deflection; and

FIG. 17 is a representative graph showing stress versus deflection

It is to be noted that the drawings illustrate only typical embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention encompasses other equally effective embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Young's Modulus is a measurement of elasticity, which is defined by the ratio of axial stress to axial strain. The elastic nature exhibited by cement under stress, but prior to mechanical failure, is as important for long-term annular isolation, as the actual maximum stress at which mechanical failure ultimately occurs. FIG. 1 shows an embodiment of a flexural/tensile tester 10, which provides a means to combine static flexural/tensile strength testing and elasticity measurements of cements. As configured in the Figure, the tester 10 is configured for testing tensile strength, but can be modified to test flexural strength.

As previously discussed, most cements fail in the annulus of a well while under tension, or a combination of tension and compression. The ratio of axial stress to axial strain is therefore an important factor when the axial stress is in tension, or a combination of tension and compression.

The tester 10 may utilize a beam loading system for automatic testing of cement specimens 11 in flexure and for tensile tests. This tester 10 has a traveling weight 12, which is driven by electric motor across the beam 13 of the tester 10 to produce a constant rate of loading on the specimen 11. The beam 13 has dual scales. As depicted in FIG. 1, the tester 10 is a flexural/tensile tester made by Gilson Company. Those skilled in the art will recognize that any tester capable of flexural and tensile testing is with the scope of the invention. In this embodiment of the tester 10, the traveling weight 12 automatically stops upon specimen 11 failure and load is read directly from the applicable scale on the beam 13.

A sensor 14 is positioned in contact with the tester 10 such that the displacement may be measured and recorded. In the diagram shown herein, a computer 15 records the displacement measurements. This allows for calculations based not only of the force exerted at the time of failure of the specimen 11, but the displacement at the time of failure. The tester 10 provides a constant rate of loading, so the computer 15 may also plot the displacement versus time and/or calculate the loading versus displacement for a variety of calculations. A tester 10 can be used to generate Young's Modulus values for different cement compositions under stresses that are similar to the conditions occurring in an actual wellbore in a pressurized configuration.

The present invention includes the development of a testing apparatus that enables the user to first cure specimens 11 from a liquid state, and then determine the mechanical properties such as tensile strength and stress/strain relationships of various cement slurry systems through non-ultrasonic, destructive methods, while maintaining confining pressure and temperature on the cement specimens for the duration of the curing and testing process. It is within the scope of the invention that the present apparatus allows for a more accurate testing of mechanical properties of oil and gas well cements to ensure the long term integrity of the cement sheath in a well bore for the entire operation life of a given well.

As shown in FIG. 2, the cement specimen 11 is poured into a mold 19 having three sections: a mold stationary section 20, a mold floating section 21, and a mold follower section 22. The mold 19 can be inserted into a pressure chamber capable of simulating the temperature and pressure found in the wellbore environment. Pressures up to 3,000 psi and temperatures up to 500° F. can be encountered in this environment. Those skilled in the art will recognize that the current invention is capable of being used at any pressure greater than atmospheric pressure and with a temperature range of about 32° F. to about 500° F. By curing and then testing the specimen 11 under the temperature and pressure conditions found in a wellbore, it is possible to obtain more accurate data related to the strength of the specimen 11. As shown, specimen 11 is poured or formed in a shape similar to the one depicted in FIG. 2.

The follower portion 22 of the mold 19 is bolted or otherwise attached to the follower 23 at bolt locations 24. Moreover, alignment pins 25 align the mold stationary section 20, a mold floating section 21, and a mold follower section 22. Additionally, the mold stationary section 20 is bolted to the mold base 30, shown in FIG. 3 by base bolts 26. In operation, follower 23 pulls the mold follower section 22 away from the mold stationary section 20 and the mold floating section 21. The mold floating section 21 is designed to not exert any force of the specimen during testing. The mold stationary section 20, bolted to the mold base 30, remains stationary during testing.

Referring to FIG. 3, the mold base 30 is shown in greater detail. The base bolts 26, which connect the mold base 30 to the stationary section 20 of the mold 19, are shown. Moreover, the mold base 30 is anchored to railings 31. As shown in greater detail below, these railings 31 are anchored to the testing vessel and do not allow any movement.

FIG. 4 shows the cam 40. Cam assembly bolt 41 secures the top and bottom plate of cam 40. The cam 40 pushes against the follower 23 at a front edge 42 of the cam 40. During testing, the cam 40 provides an equal force of pressure against the follower 23, which is imparted on the specimen 11 via the follower section 22 of the mold 19.

The fully assembled mold is shown in FIG. 5. The cement specimen 11 is in the mold stationary section 20, the mold floating section 21, and the mold follower section 22. The follower portion 22 is bolted or otherwise attached to the follower 23 at bolt locations 24. Alignment pins 25 align the mold stationary section 20, the mold floating section 21, and the mold follower section 22. Additionally, the mold stationary section 20 is bolted to the mold base 30, shown in FIG. 3 by base bolts 26.

This assembly view shows how the follower 23 can pulls the mold follower section 22 away from the mold stationary section 20 and the mold floating section 21 during testing. The base bolts 26 hold the stationary portion 20 in place as the follower 23 is pushed at the front edge 40 of the cam 40. Cam assembly bolts 41 bolt the cam 40.

This movement is also shown in the side view of the assembly of FIG. 6. The mold stationary section 20, the mold floating section 21, and the mold follower section 22 are shown such that the mold follower section 22 is attached to the follower 23 by bolt 24. The mold stationary section 20 is bolted to the mold base 30 base bolt 26. Cam 40 pushes follower 23, which in turn pulls the mold follower section 22.

Turning to FIG. 7, a plurality of testers are shown connected to the railing 31 within a pressure chamber 80, which is used to simulate the temperature and pressure encountered in the wellbore. Piston 70 is disposed through cover 75 of the pressure chamber 80. The piston 70 is moved by a short stroke hydraulic ram 74 or similar device. Precision linear transducers 71, 72 are positioned on opposite sides of the piston 70 to ensure even travel of the piston 70 in to the pressure chamber 80 and to measure the displacement of the cam. A load cell 73 is disposed therein to measure to the amount of force applied by the ram 74.

A thermocouple 76 and a pressure transducer 77 are connected to the pressure chamber 80. Data from the precision linear transducers 71, 72, the thermocouple 76, and the pressure transducer 77 are provided to a data acquisition unit 78.

Those skilled in the art recognize the benefits of this configuration. Cement specimens 11 are placed in molds 30 within the pressure chamber 80. A pressure medium 79, such as fresh water or mineral oil, is introduced to pressurize the system to the temperature and pressure levels that would be encountered in a wellbore environment. The cement specimens 11 are allowed to cure at these temperatures and pressures, as each would under wellbore conditions. Once cured, each specimen 11 is tested using the ram 74 to push the piston 70 such that each specimen 11 is sequentially stressed until failure.

The piston pushes the first cam until the cement specimen 11 fails. The data acquisition unit 78 constantly monitors the precision linear transducers 71, 72, the thermocouple 76, and the pressure transducer 77, collecting data throughout the process. It is important to arrange each mold with enough axial distance such that the failure of each cement specimen will not cause the next follower to be bumped with a breaking force. By axially spacing the cams such that the first specimen fails, the piston ushers the cam forward to smoothly interface with the next cam. The next sample may be stretched in a sequential fashion.

Once the second specimen fails, another axial gap exists such that the rapid expansion of the cams will not strike the third mold. Though three molds are shown in FIG. 7, those skilled in the art will recognize that any plurality of molds within at least one pressure chamber is considered to be within the scope of the invention.

FIG. 8 shows a cross-sectional view of the pressure chamber 80. The pressurizing medium 79 surrounds the testing apparatus. The rails 31 are connected the mold base 30, wherein the pulled portion of the mold 22 is shown on top of the mold base 30. The cam 40 is shown above and below the mold base 30. This arrangement shows how the cam 40 urges the pulled portion of the mold 22 toward the viewer, thus stressing the cement specimen in the mold until failure.

EXAMPLES

Three cement specimens were cured at atmospheric pressure, 198° F., and 20.0 ppg. The slurry design was used for this experiment was primarily Norcem AS G with 45% W-10+20% MPA-3+0.01797 gps CD-31L+0.0839 pgs R-15L+0.0 gps FP-6L. A maximum cycle load of 5000 N (2027 psi) was applied.

The deflection versus time graph in FIG. 9 shows the consistency of the deflection of the samples prior to failure. The peaks of the graphs are very similar and the time to failure of the three samples has a similar width on the X-axis.

FIG. 10 shows the flexural stress (psi) versus the deflection (inches) for one of these samples. The linear increase of deflection as the stress increased shows the consistency of the results. When the deflection is compared to the Young's Modulus, as shown in FIG. 11, the graph shows the flattening the Young's modulus as the sample's deflection nears the failure point.

Two additional samples are shown in FIG. 11 in a tensile strength test. Using the same slurry, a maximum cycle load of 3900 N (878 psi) with an actual failure load of 4725 N (1064 psi) was applied. Again, the consistency of the shape of the peaks and width of the results on the X-axis show the preciseness of the tester in this analysis. The graph in FIG. 12 shows the tensile stress versus the deflection of the sample under tension only. This is in comparison with FIG. 13 that shows the tensile strength test of the stress versus the microstrain.

In another experiment, Calport H cement was mixed at 16.5 ppg and cured for about 48 hours at atmospheric temperature and pressure. The following table depicts the three specimens as stress using the above-disclosed tester was applied on each specimen. The deflection was measured using the precision linear transducers listed above. TABLE 1 Calport H Stress v. Deflection Testing Time Deflect 1 Stress 1 Deflect 2 Stress 2 Deflect 3 Stress 3 (sec) (inches) (psi) (inches) (psi) (inches) (psi) 0 0 0 0 0 0 0 1.002 0 0 0 0 0 0 1.998 0 0 0 0 0 −5.775096 3.000 0 0 0 0 0 0 4.002 0 0 0 0 0 0 4.998 0 0 0 0 0 0 6.000 0 0 0 0 0 5.775096 7.000 0 5.775096 0 11.550184 0 5.775096 8.000 0 5.775096 0 11.550184 0 11.550184 9.000 0 11.550192 0 11.550184 0 11.550184 10.000 0 17.32528 0 17.32528 0 17.32528 11.000 0 17.32528 0 17.32528 0 17.32528 12.000 0 23.100376 0 23.100376 0 23.100376 13.000 0 23.100376 0 28.875464 0.0001 28.875472 14.000 0 28.875472 0 28.875464 0 28.875472 15.000 0 28.875472 0 28.875464 0.0001 28.875472 16.000 0 28.875472 0 34.6505616 0.0001 34.65056 17.000 0 34.650568 0 34.6505616 0.0001 34.65056 18.000 0 34.650568 0 40.425656 0.0001 34.65056 19.000 0 34.650568 0 40.425656 0.0001 34.65056 20.000 0 40.425656 0 40.425656 0.0001 40.4256576 21.000 0 40.425656 0 46.2007504 0.0001 46.200752 22.000 0 40.425656 0 46.2007504 0.0001 46.200752 23.000 0 46.2007536 0.0001 51.975848 0.0001 51.9758464 24.000 0.0001 46.2007536 0.0001 51.975848 0.0001 57.750944 25.000 0.0001 51.975848 0.0001 57.750936 0.0001 57.750944 26.000 0.0001 51.975848 0.0001 57.750936 0.0005 63.526032 27.000 0.0001 57.7509424 0.0001 63.526032 0.0006 69.301128 28.000 0.0001 57.7509424 0.0001 63.526032 0.0008 69.301128 29.000 0.0001 63.52604 0.0004 63.526032 0.0009 69.301128 30.000 0.0001 63.52604 0.0004 69.301128 0.001 75.076224 31.000 0.0001 69.301128 0.0005 69.301128 0.0012 75.076224 32.000 0.0001 75.076224 0.0006 75.076224 0.0013 80.85132 33.000 0.0001 75.076224 0.0007 75.076224 0.0014 80.85132 34.000 0.0004 75.076224 0.0008 80.851312 0.0016 86.626408 35.000 0.0004 75.076224 0.0009 86.626408 0.0017 92.401504 36.000 0.0005 80.85132 0.001 92.401504 0.0018 92.401504 37.000 0.0006 80.85132 0.0011 92.401504 0.002 98.1766 38.000 0.0007 86.626416 0.0013 92.401504 0.0021 98.1766 39.000 0.0008 92.401504 0.0013 98.1766 0.0023 103.951696 40.000 0.001 92.401504 0.0015 98.1766 0.0024 103.951696 41.000 0.001 98.1766 0.0015 103.951696 0.0025 103.951696 42.000 0.0012 103.951696 0.0017 103.951696 0.0026 109.726792 43.000 0.0013 103.951696 0.0017 109.726784 0.0027 115.50188 44.000 0.0013 103.951696 0.0019 109.726784 0.0029 115.50188 45.000 0.0015 109.726792 0.0019 115.50188 0.003 121.276976 46.000 0.0016 109.726792 0.0021 115.50188 0.0031 121.276976 47.000 0.0017 115.501888 0.0021 121.276984 0.0033 121.276976 48.000 0.0019 121.276976 0.0022 121.276984 0.0034 127.05208 49.000 0.002 121.276976 0.0024 127.052104 0.0035 127.05208 50.000 0.0021 127.052072 0.0024 132.827144 0.0037 138.60224 51.000 0.0022 127.052072 0.0026 132.827144 0.0038 138.60224 52.000 0.0023 127.052072 0.0027 132.827144 0.004 138.60224 53.000 0.0025 132.827176 0.0028 138.602264 0.0041 138.60224 54.000 0.0025 132.827176 0.0029 138.602264 0.0042 144.37736 55.000 0.0027 144.377336 0.0031 144.377384 0.0043 150.15248 56.000 0.0028 144.377336 0.0031 150.152424 0.0044 155.92752 57.000 0.003 144.377336 0.0033 150.152424 0.0045 155.92752 58.000 0.0031 144.377336 0.0034 150.152424 0.0047 155.92752 59.000 0.0031 150.152456 0.0036 155.927544 60.000 0.0033 155.927576 0.0036 155.927544 61.000 0.0038 161.702664 62.000 0.0039 161.702664 63.000 0.0041 167.477704 64.000 0.0042 167.477704

As shown in this table, the first and third specimens bear similar results, namely 155.927 psi with 0.0033 inches deflection and 0.0047 inches deflection, respectively while the second specimen bears 167.478 psi and 0.0042 inches deflection. The data for the second and third specimens have been graphed in FIG. 15. The closeness of this data indicates the consistency of the testing technique. It is envisioned that this consistency will be seen in pressurized experiments.

In another experiment, Calport G cement was mixed at 15.8 ppg and cured for about 48 hrs at 130° F. and atmospheric pressure. Two specimens were tested: TABLE 2 Calport G Stress v. Deflection Testing Time Deflect 2 Stress 2 Stress 1 (sec) (inches) (psi) Deflect 1 (psi) 1 0 21.787232 0 21.787232 2 0 21.787232 0 21.787232 3 0 21.787232 0 21.787232 4 0 21.787232 0 21.787232 5 0 21.787232 0 21.787232 6 0 21.787232 0 21.787232 7 0 21.787232 0 21.787232 8 0 21.787232 0 21.787232 9 0 21.787232 0 21.787232 10 0 27.23404 0 21.787232 11 0 32.680856 0 27.23404 12 0 32.680856 0 27.23404 13 0 38.127664 0 32.680856 14 0 43.574472 0 38.127664 15 0 43.574472 0 38.127664 16 0 43.574472 0 43.574472 17 0 49.02128 0 43.574472 18 0 49.02128 0 43.574472 19 0 49.02128 0 43.574472 20 0 54.468088 0 49.02128 21 0 59.914896 0 54.468088 22 0 59.914896 0 54.468088 23 0 59.914896 0 59.914896 24 0 65.361704 0 59.914896 25 0 65.361704 0 59.914896 26 0 70.808512 0 65.361704 27 0 70.808512 0 65.361704 28 0 76.25532 0 70.808512 29 0 76.25532 0 70.808512 30 0 81.70216 0 76.25532 31 0 81.70216 0 76.25532 32 0 81.70216 0 81.70216 33 0 87.14896 0 81.70216 34 0 87.14896 0 87.14896 35 0 92.59576 0 87.14896 36 0 98.04256 0 92.59576 37 0 98.04256 0 92.59576 38 0 98.04256 0 98.04256 39 0 103.48936 0 98.04256 40 0 103.48936 0 98.04256 41 0 108.93616 0 98.04256 42 0.0001 108.93616 0 103.48936 43 0.0001 114.38296 0 103.48936 44 0.0001 114.38296 0 108.93616 45 0.0001 119.82976 0 108.93616 46 0.0001 119.82976 0 114.38296 47 0.0001 125.27656 0 114.38296 48 0.0001 125.27656 0 119.82976 49 0.0004 130.72344 0 119.82976 50 0.0005 136.17024 0 119.82976 51 0.0005 136.17024 0 125.27656 52 0.0005 136.17024 0 125.27656 53 0.0006 141.61704 0.0001 130.72344 54 0.0007 147.06384 0.0001 136.17024 55 0.0007 147.06384 0.0001 136.17024 56 0.0008 152.51064 0.0001 141.61704 57 0.0009 152.51064 0.0009 147.06384 58 0.0009 157.95744 0.001 147.06384 59 0.001 157.95744 0.001 152.51064 60 0.001 163.40424 0.001 152.51064 61 0.0011 163.40424 0.001 152.51064 62 0.0011 168.85104 0.001 157.95744 63 0.0012 168.85104 0.001 157.95744 64 0.0013 174.29784 0.001 163.40424 65 0.0013 174.29784 0.0013 163.40424 66 0.0014 179.74472 0.0013 168.85104 67 0.0015 179.74472 0.0013 174.29784 68 0.0016 185.19152 0.0013 174.29784 69 0.0017 185.19152 0.0014 174.29784 70 0.0017 185.19152 0.0014 179.74472 71 0.0018 185.19152 0.0015 185.19152 72 0.0019 190.63832 0.0015 185.19152 73 0.0019 190.63832 0.0016 185.19152 74 0.002 196.08512 0.0016 185.19152 75 0.0021 196.08512 0.0017 185.19152 76 0.0022 201.53192 0.0017 190.63832 77 0.0023 201.53192 0.0018 196.08512 78 0.0023 206.97872 0.0019 196.08512 79 0.0024 206.97872 0.002 201.53192 80 0.0025 212.42552 0.002 201.53192 81 0.0026 212.42552 0.0021 201.53192 82 0.0027 212.42552 0.0022 206.97872 83 0.0028 217.87232 0.0022 212.42552 84 0.0028 217.87232 0.0023 212.42552 85 0.0029 223.3192 0.0023 212.42552 86 0.003 223.3192 0.0025 217.87232 87 0.0031 228.766 0.0025 217.87232 88 0.0032 228.766 0.0026 223.3192 89 0.0032 228.766 0.0027 223.3192 90 0.0033 234.2128 0.0027 223.3192 91 0.0034 234.2128 0.0028 228.766 92 0.0035 239.6596 0.0029 228.766 93 0.0036 239.6596 0.003 234.2128 94 0.0037 239.6596 0.0031 234.2128 95 0.0038 245.1064 0.0032 239.6596 96 0.0039 250.5532 0.0032 239.6596 97 0.0039 250.5532 0.0033 239.6596 98 0.0041 250.5532 0.0034 245.1064 99 0.0041 256 0.0035 250.5532 100 0.0042 256 0.0036 250.5532 101 0.0043 256 0.0037 250.5532 102 0.0044 261.4468 0.0038 256 103 0.0045 261.4468 0.0039 256 104 0.0046 266.8936 0.004 261.4468 105 0.0047 266.8936 0.004 261.4468 106 0.0048 266.8936 0.0042 266.8936 107 0.0049 272.3404 0.0042 266.8936 108 0.005 272.3404 0.0044 266.8936 109 0.0051 277.7872 0.0044 272.3404 110 0.0052 277.7872 0.0046 272.3404 111 0.0053 277.7872 0.0046 272.3404 112 0.0054 283.23408 0.0047 277.7872 113 0.0055 283.23408 0.0048 277.7872 114 0.0056 288.68088 0.0049 283.23408 115 0.0057 288.68088 0.005 283.23408 116 0.0058 294.12768 0.0051 288.68088 117 0.0059 294.12768 0.0052 288.68088 118 0.006 294.12768 0.0053 294.12768 119 0.0061 294.12768 0.0054 294.12768 120 0.0062 299.57448 0.0055 294.12768 121 0.0063 305.02128 0.0056 299.57448 122 0.0064 305.02128 0.0058 299.57448 123 0.0065 305.02128 0.0058 305.02128 124 0.0066 310.46808 0.006 305.02128 125 0.0067 310.46808 0.006 305.02128 126 0.0068 315.91488 0.0062 310.46808 127 0.0069 315.91488 0.0062 310.46808 128 0.007 315.91488 0.0064 315.91488 129 0.0071 321.36168 0.0064 315.91488 130 0.0072 326.80856 0.0067 315.91488 131 0.0073 326.80856 0.0067 321.36168 132 0.0074 326.80856 0.0069 326.80856 133 0.0075 326.80856 0.007 326.80856 134 0.0076 332.25536 0.0072 326.80856 135 0.0077 332.25536 0.0073 332.25536 136 0.0078 332.25536 0.0074 332.25536 137 0.0079 337.70216 0.0075 332.25536 138 0.008 343.14896 0.0076 337.70216 139 0.0081 343.14896 0.0078 337.70216 140 0.0082 348.59576 0.0079 343.14896 141 0.0083 348.59576 0.0081 348.59576 142 0.0084 348.59576 0.0083 348.59576 143 0.0086 348.59576 0.0085 348.59576 144 0.0087 348.59576 0.0086 348.59576 145 0.0088 348.59576 0.0088 348.59576 146 0.0089 348.59576 0.0093 348.59576 147 0.0091 354.04256 0.0093 348.59576 148 0.0092 359.48936 0.0097 354.04256 149 0.0093 359.48936 0.0098 354.04256 150 0.0094 364.93616 0.0102 359.48936 151 0.0096 364.93616 0.0104 359.48936 152 0.0097 364.93616 0.0107 364.93616 153 0.0098 370.38296 0.0111 364.93616 154 0.0099 370.38296 0.0114 364.93616 155 0.0101 370.38296 0.0119 364.93616 156 0.0102 375.82976 0.0125 370.38296 157 0.0103 375.82976 0.0126 370.38296 158 0.0104 381.27664 0.0134 370.38296 159 0.0106 381.27664 0.0136 375.82976 160 0.0107 386.72344 0.0142 381.27664 161 0.0109 386.72344 0.0146 381.27664 162 0.011 386.72344 163 0.0111 392.17024 164 0.0113 392.17024 165 0.0114 392.17024 166 0.0115 397.61704 167 0.0116 397.61704 168 0.0118 397.61704 169 0.0119 403.06384 170 0.012 403.06384 171 0.0121 408.51064 172 0.0122 408.51064 173 0.0124 408.51064 174 0.0125 413.95744 175 0.0126 413.95744 176 0.0126 419.40424 177 0.0128 419.40424 178 0.0129 419.40424 179 0.013 424.85104 180 0.0131 424.85104 181 0.0132 430.29792 182 0.0133 430.29792 183 0.0134 430.29792 184 0.0135 430.29792 185 0.0136 435.74464

As shown in this table, the first specimen bore 381.276 psi and 0.0146 inches deflection while the second specimen boar 435.745 psi and 0.0136 inches deflection. The data for the first and second specimens have been graphed in FIG. 16. The closeness of this data indicates the consistency of the testing technique. It is envisioned that this consistency will be seen in pressurized experiments.

In another experiment, Calport G cement was mixed at 15.8 ppg and cured for about 48 hrs at 130° F. and atmospheric pressure. Two specimens were tested. TABLE 3 Second Calport G Stress v. Deflection Testing Time Deflection 2 Stress 2 Deflection 1 Stress 1 (sec) (inches) (psi) (inches) (psi) 0 0.000 10.894 0.0000 21.79 1.000 0.000 10.894 0.0000 21.79 2.000 0.000 10.894 0.0000 21.79 3.000 0.000 16.340 0.0000 21.79 4.000 0.000 16.340 0.0000 21.79 5.000 0.000 16.340 0.0000 21.79 6.000 0.000 16.340 0.0000 21.79 7.000 0.000 21.787 0.0000 27.23 8.000 0.000 21.787 0.0000 27.23 9.000 0.000 21.787 0.0000 32.68 10.000 0.000 21.787 0.0000 38.13 11.000 0.000 27.234 0.0000 38.13 12.000 0.000 27.234 0.0000 43.57 13.000 0.000 27.234 0.0000 49.02 14.000 0.000 32.681 0.0000 49.02 15.000 0.000 38.128 0.0000 49.02 16.000 0.000 38.128 0.0000 54.47 17.000 0.001 43.574 0.0000 54.47 18.000 0.001 43.574 0.0000 59.91 19.000 0.001 49.021 0.0000 59.91 20.000 0.001 54.468 0.0000 59.91 21.000 0.001 59.915 0.0000 59.91 22.000 0.001 59.915 0.0000 65.36 23.000 0.001 65.362 0.0000 70.81 24.000 0.001 70.809 0.0000 76.26 25.000 0.001 70.809 0.0000 76.26 26.000 0.001 76.255 0.0000 76.26 27.000 0.001 81.702 0.0001 76.26 28.000 0.001 81.702 0.0001 81.70 29.000 0.001 81.702 0.0001 87.15 30.000 0.001 87.149 0.0001 87.15 31.000 0.001 87.149 0.0001 87.15 32.000 0.001 92.596 0.0001 92.60 33.000 0.001 98.043 0.0001 98.04 34.000 0.002 98.043 0.0001 98.04 35.000 0.002 103.489 0.0001 98.04 36.000 0.002 103.489 0.0001 98.04 37.000 0.002 108.936 0.0001 103.49 38.000 0.002 114.383 0.0001 108.94 39.000 0.002 114.383 0.0003 114.38 40.000 0.002 119.830 0.0004 114.38 41.000 0.002 119.830 0.0005 114.38 42.000 0.002 119.830 0.0006 119.83 43.000 0.002 119.830 0.0006 119.83 44.000 0.002 125.277 0.0007 125.28 45.000 0.002 130.723 0.0007 125.28 46.000 0.002 130.723 0.0008 136.17 47.000 0.002 136.170 0.0008 136.17 48.000 0.002 136.170 0.0009 136.17 49.000 0.002 141.617 0.0010 136.17 50.000 0.003 141.617 0.0011 136.17 51.000 0.003 147.064 0.0012 136.17 52.000 0.003 147.064 0.0013 147.06 53.000 0.003 152.511 0.0014 147.06 54.000 0.003 152.511 0.0015 152.51 55.000 0.003 152.511 0.0016 152.51 56.000 0.003 157.957 0.0017 157.96 57.000 0.003 157.957 0.0018 157.96 58.000 0.003 163.404 0.0019 163.40 59.000 0.003 163.404 0.0020 163.40 60.000 0.003 168.851 0.0021 168.85 61.000 0.003 168.851 0.0022 168.85 62.000 0.003 174.298 0.0023 174.30 63.000 0.003 174.298 0.0025 174.30 64.000 0.004 179.745 0.0026 179.74 65.000 0.004 179.745 0.0027 179.74 66.000 0.004 185.192 0.0028 179.74 67.000 0.004 185.192 0.0029 185.19 68.000 0.004 190.638 0.0031 190.64 69.000 0.004 190.638 0.0032 190.64 70.000 0.004 190.638 0.0033 190.64 71.000 0.004 196.085 0.0035 196.09 72.000 0.004 196.085 0.0035 196.09 73.000 0.004 196.085 0.0037 201.53 74.000 0.004 201.532 0.0038 201.53 75.000 0.004 201.532 0.0038 201.53 76.000 0.004 206.979 0.0041 206.98 77.000 0.004 206.979 0.0041 206.98 78.000 0.005 212.426 0.0043 212.43 79.000 0.005 212.426 0.0043 212.43 80.000 0.005 212.426 0.0045 212.43 81.000 0.005 217.872 0.0045 217.87 82.000 0.005 217.872 0.0047 217.87 83.000 0.005 223.319 0.0048 223.32 84.000 0.005 223.319 0.0049 223.32 85.000 0.005 223.319 0.0050 223.32 86.000 0.005 228.766 0.0052 228.77 87.000 0.005 228.766 0.0052 228.77 88.000 0.005 234.213 0.0054 234.21 89.000 0.005 234.213 0.0055 234.21 90.000 0.006 234.213 0.0056 234.21 91.000 0.006 239.660 0.0057 239.66 92.000 0.006 239.660 0.0058 239.66 93.000 0.006 245.106 0.0059 245.11 94.000 0.006 245.106 0.0060 250.55 95.000 0.006 250.553 0.0062 250.55 96.000 0.006 250.553 0.0063 250.55 97.000 0.006 250.553 0.0063 250.55 98.000 0.006 256.000 0.0065 256.00 99.000 0.006 256.000 0.0066 256.00 100.000 0.006 261.447 0.0068 261.45 101.000 0.006 261.447 0.0069 261.45 102.000 0.007 261.447 0.0071 266.89 103.000 0.007 266.894 0.0071 266.89 104.000 0.007 272.340 0.0074 266.89 105.000 0.007 272.340 0.0075 272.34 106.000 0.007 272.340 0.0077 272.34 107.000 0.007 277.787 0.0079 272.34 108.000 0.007 283.234 0.0080 277.79 109.000 0.007 283.234 0.0084 277.79 110.000 0.007 283.234 0.0086 277.79 111.000 0.007 283.234 0.0090 283.23 112.000 0.008 283.234 0.0092 283.23 113.000 0.008 283.234 0.0097 288.68 114.000 0.008 288.681 0.0099 288.68 115.000 0.008 288.681 0.0103 288.68 116.000 0.008 294.128 0.0106 294.13 117.000 0.008 294.128 0.0110 294.13 118.000 0.008 294.128 0.0112 294.13 119.000 0.008 299.574 0.0116 299.57 120.000 0.009 299.574 0.0117 305.02 121.000 0.009 299.574 0.0122 305.02 122.000 0.009 305.021 0.0123 305.02 123.000 0.009 305.021 0.0125 305.02 124.000 0.009 310.468 0.0127 305.02 125.000 0.009 310.468 0.0130 310.47 126.000 0.010 310.468 0.0131 310.47 127.000 0.010 315.915 0.0135 315.91 128.000 0.010 315.915 0.0136 315.91 129.000 0.010 315.915 0.0138 315.91 130.000 0.010 321.362 0.0139 321.36 131.000 0.011 321.362 0.0141 326.81 132.000 0.011 326.809 0.0142 326.81 133.000 0.011 326.809 0.0144 326.81 134.000 0.011 332.255 0.0145 332.26 135.000 0.011 332.255 0.0147 332.26 136.000 0.012 332.255 0.0149 332.26 137.000 0.012 337.702 0.0149 332.26 138.000 0.012 337.702 0.0152 337.70 139.000 0.012 337.702 0.0153 337.70 140.000 0.012 343.149 0.0155 343.15 141.000 0.012 348.596 0.0156 343.15 142.000 0.013 348.596 0.0157 348.60 143.000 0.013 348.596 0.0158 348.60 144.000 0.013 348.596 0.0160 348.60 145.000 0.013 354.043 0.0161 348.60 146.000 0.013 354.043 0.0163 354.04 147.000 0.013 359.489 0.0164 359.49 148.000 0.013 359.489 0.0166 359.49 149.000 0.014 364.936 0.0167 359.49 150.000 0.014 364.936 0.0168 364.94 151.000 0.014 364.936 0.0169 364.94 152.000 0.014 370.383 0.0171 370.38 153.000 0.014 370.383 0.0172 370.38 154.000 0.014 370.383 0.0173 370.38 155.000 0.014 375.830 0.0175 370.38 156.000 0.014 375.830 0.0176 370.38 157.000 0.015 381.277 0.0177 375.83 158.000 0.015 381.277 0.0178 375.83 159.000 0.015 381.277 0.0179 381.28 160.000 0.015 386.723 0.0180 381.28 161.000 0.015 386.723 0.0181 386.72 162.000 0.015 386.723 0.0182 386.72 163.000 0.015 392.170 0.0183 386.72 164.000 0.015 392.170 0.0185 392.17 165.000 0.015 397.617 0.0185 392.17 166.000 0.016 397.617 0.0187 392.17 167.000 0.016 397.617 0.0187 397.62 168.000 0.016 403.064 169.000 0.016 403.064 170.000 0.016 403.064 171.000 0.016 408.511 172.000 0.016 408.511 173.000 0.016 408.511 174.000 0.016 413.957 175.000 0.016 413.957 176.000 0.016 413.957 177.000 0.017 419.404 178.000 0.017 419.404 179.000 0.017 419.404 180.000 0.017 424.851 181.000 0.017 424.851 182.000 0.017 430.298 183.000 0.017 430.298 184.000 0.017 430.298 185.000 0.017 435.745 186.000 0.017 435.745 187.000 0.018 441.192 188.000 0.018 441.192 189.000 0.018 441.192 190.000 0.018 446.638 191.000 0.018 446.638

As shown in this table, the first specimen bore 397.62 psi and 0.0187 inches deflection while the second specimen boar 446.638 psi 0.018 inches deflection. The data for the first and second specimens have been graphed in FIG. 17. Again, the closeness of this data indicates the consistency of the testing technique. It is envisioned that this consistency will be seen in pressurized experiments.

Those skilled in the art will recognize that the present testing method and apparatus are applicable to any type of cement or cement composition. Examples of suitable hydraulic cement types that may be employed, alone or in mixtures, for wellbore cementing include Portland cements, and more particularly ASTM Type I, II, III, IV and/or V Portland cements, and API Class A, B, C, G and/or H Portland cements, pozzolan cements, Portland cement blends, commercial lightweight cements, slag cements, and microfine cements. Any natural or synthetic material that is substantially elastic, and more particularly that is selected to be substantially elastic under in situ cementing conditions (e.g., downhole well cementing conditions), may be employed. Such materials may be employed in particulate form, and may have individual particles of material may have shapes such as beaded, regular, or irregular shapes, or mixtures thereof. Examples of substantially elastic materials include, but are not limited to, those elastic materials having a Young's modulus of elasticity between about 500 psi and about 2,600,000 psi at anticipated cementing conditions, alternatively between about 500 psi and about 2,000,000 psi at anticipated cementing conditions, alternatively between about 5,000 psi and about 2,000,000 psi at anticipated cementing conditions, alternatively between about 5,000 psi and about 500,000 psi at anticipated cementing conditions, alternatively between about 5,000 psi and 200,000 psi at anticipated cementing conditions, and further alternatively between about 7,000 and 150,000 psi at anticipated cementing conditions. Other examples of substantially elastic materials include, but are not limited to, those elastic materials having a Young's modulus of elasticity between about 500 psi and about 30,000,000 psi at anticipated cementing conditions, alternatively between about 2,000,000 psi and about 30,000,000 psi at anticipated cementing conditions, alternatively between about 2,000,000 psi and about 10,000,000 psi at anticipated cementing conditions, alternatively between about 5,000 psi and about 5,000,000 psi at anticipated cementing conditions, and alternatively between about 7,000 psi and about 1,500,000 psi at anticipated cementing conditions. Yet other examples of substantially elastic materials include, but are not limited to, those elastic materials having a Young's modulus of elasticity between about 500 psi and about 150,000 psi at anticipated cementing conditions. Substantially elastic materials may also have values of Young's modulus of elasticity that are greater than or lesser than those values given in the ranges above.

Having described the invention above, various modifications of the techniques, procedures, material and equipment will be apparent to those in the art. It is intended that all such variations within the scope and spirit of the appended claims be embraced thereby. 

1. A method of determining a Young's modulus of a cement specimen, the method comprising the steps of: (a) inserting cement into a cement mold inside a pressure vessel; (b) increasing the pressure and temperature within the vessel; (c) allowing the specimen to cure to form the cement specimen; (d) applying a measured axial stress and axial strain tension to the specimen; and (e) determining a ratio of axial stress to axial strain in the specimen wherein the ratio is the Young's modulus of the spectrum.
 2. The method of claim 1 which further comprises the steps of measuring the deflection of the specimen during Step (d).
 3. The method of claim 1 wherein the pressure vessel is at a pressure greater than atmospheric after Step (b).
 4. The method of claim 1 wherein the pressure vessel is at a temperature from a range of about 32° F. to about 500° F. after Step (b).
 5. The method of claim 1, which further comprises the step of using a data acquisition unit to accumulate data during Step (d).
 6. A method of determining a plurality of Young's moduluses for a corresponding plurality of cement specimens, the method which comprises using the Method of claim 1 to determine the Young's modulus on each corresponding specimen.
 7. The method of claim 2, wherein the deflection is measure by at least one precision linear transducer. 8-15. (canceled)
 16. A method of determining Young's modulus in a cement specimen, comprising the steps of: (a) determining axial stress in the specimen; (b) determining axial strain in the specimen; and (c) determining the ratio of axial stress to axial strain in the specimen to find the Young's modulus; wherein Step (a) does not include determining axial stress by compressing the specimen.
 17. The method of claim 16, the method which comprises pressurizing the specimen prior to Step (a).
 18. The method of claim 16, wherein Step (a) measures a tensional stress.
 19. A method of determining a plurality of Young's moduluses for a corresponding plurality of cement specimens, which comprises using the method of claim 16 for each specimen, wherein each specimen is contained in a single pressure vessel. 